Noncrumbling eraser composed of rubber, polyisobutylene and an abrasive material



United States NONCRUMBLING ERASER COMPOSED OF RUB- BER, POLYISOBUTYLENE AND AN ABRASIVE MATERIAL Charles L. Smith and Benson G. Brand, Columbus, Ohio,

assiguors, by mesne assignments, to Mrs. Naomi Burrows, Columbus, Ohio No Drawing. Application February 14, 1957 Serial No. 640,087

7 Claims. (Cl. 51-298) This invention relates to an improved eraser. More specifically, it relates to an eraser that will cleanly erase typewriter and pencil impressions.

To erase typewriter copy, pencil marks, etc., from paper, it is necessary to remove a quantity of the paper, in that the carbon of the pencil or the carbon and dye of the typewriter ribbon penetrates into the paper itself. The quantity or depth of paper that must be removed depends upon the depth of penetration. Typewriter copy presents a much deeper penetration of carbon into the paper and requires more abrasion to remove it. Thus a harder, more abrasive eraser is required. Prior art erasers, whether they are hard, such as typewriter erasers, or soft, such as ordinary pencil erasers, perform their function of removing that portion of the paper exhibiting the undesired marks by abrading away the paper surface. Crumbs from the abraded paper and the eraser itself remain in the vicinity of the erasure. This is particularly the case where art-gum-type erasers are employed, in that this type of eraser produces large quantities of crumbs or refuse which are bothersome and messy to remove. Conventional typewriter erasers cause erasure refuse to fall into the typewriter mechanism itself, thus requiring frequent cleaning and repairing of typewriters to remove such material which interferes with their proper operation. In addition, eraser refuse falls between the carbon paper and the copy when using conventional typewriter erasers to correct mistakes Where copies are being made, thus causing marked and messy carbon copies. Also, such refuse is undesirable to draftsmen or other people compelled to erase the inevitable mistakes made wherever people employ pencil and paper.

An eraser has now been developed which overcomes the undesirable features of the conventional prior art erasers. This eraser, whether hard or soft, retains its crumbs when rubbed against paper. A majority of the abraded paper particles cling to the eraser block, thus minimizing the quantity of eraser refuse left behind on the paper. This eraser is particularly advantageous when employed as a typewriter eraser, in that very little eraser refuse falls into the typewriter mechanism or mars carbon copies. It has been found that, in addition to the above-mentioned advantageous features, the present eraser erases much more cleanly than prior art erasers. This is due to the fact that eraser refuse causes smearing When making erasures but, where no refuse is present no smearing occurs.

It is, therefore, the primary object of the present invention to provide an eraser that will not produce eraser refuse when used.

Another object is to provide an eraser which will remove typed letters without projecting eraser refuse into the typewriter mechanism or mar carbon copies.

Other objects and advantageous features will be apparent in the following detailed description.

In general, this invention relates to a noncrumbling eraser composed of a cured rubber composition consisting essentially of rubber, from 30 to 80 parts of polysmear what is being erased and tear the paper.

ice

isobutylene having a molecular weight not greater than 40,000, and from to 240 parts filler and abrasive materials.

A more preferred embodiment of the present invention is a noncrumbling eraser composed of a cured rubber composition consisting essentially of natural smoked rubber, from 30 to 50 parts of polyisobutylene having a molecular weight not greater than 40,000, from 60 to 120 parts abrasive material (preferably to 400-grit size) and from 80 to parts filler material.

If greater than 80 parts of polyisobutylene are employed, the eraser becomes sticky and tacky and tends to However, if less than 30 parts of polyisobutylene are employed, the eraser will not produce the significant noncrumbling characteristics. Optimum results are obtained when the range of from 30 to 50 parts is employed.

The polyisobutylene should be a polymeric material having a molecular weight not greater than 40,000 and preferably in the form ofa soft, gummy, tacky solid. Polyisobutylene having a molecular weight greater than 40,000 does not possess the soft, gummy, and tacky properties necessary to impart the noncrumbling characteristic to the eraser.

The abrasive and filler materials employed may be any of these materials used in the eraser art. Inert filler materials are commonly employed in all rubber compositions and do not serve any specific function but to supply bulk. Commonly employed inert filler materials are silica flour, calcium carbonate, chalk, talc, barytes, diatomaceous earths, certain finely divided clays, etc. Filler materials may supply a mild abrasive action in an eraser in which event they sometimes may be regarded as an abrasive. The ordinary filler material is made up of particles the average of which is not larger than 325 mesh or about 44 microns in diameter and possesses a hardness of about 6 Mohs (Mohs scale of hardness: 1, tale; 2, gypsum; 3, calcite; 4, fluorite; 5, apatite; 6, orthoclase; 7, quartz; 8, topaz; 9, corundum; 10, diamond). Such materials do not contribute significantly abrasive action. If greater than 240 parts of filler material or filler material plus abrasive material are employed, the eraser becomes crumbly.

Commonly employed abrasive materials for erasers are silicon carbide, silicon dioxide, sand, emery powder, etc. These mineral abrasive materials serve to abrade the paper and thus remove the paper containing the material being erased. In the present erasers, the material being abraded clings to the eraser block. The commonly used mineral abrasives are made of particles larger than 325 mesh or 44 microns in diameter. In the present invention, they are preferably within the range of from 100- to 400- grit and preferably possess a hardness in excess of that commonly used for filler materials. Such abrasives should possess a hardness of from 7 to 9 Mohs. The grit size of the abrasive material employed is dependent on type of material to be erased.

The amount of abrasive material required is dependent upon the type of eraser being made (pencil erasers, typewriter erasers, etc.). At least 60 parts of abrasive, or filler, or combinations of both, and not over 240 parts of abrasive plus filler should be present. Best results are obtained when the eraser contains 60 to 120 parts of abrasive material and from 80 to 120 parts of filler material. It has also been found preferable to use an abrasive with a grit size of from 100- to 400-grit. Best results have been obtained with ISO-grit material.

It may be preferable to add a white pigment .to lighten the color of the eraser, and titanium dioxide has proved to be especially effective for this purpose. However, other pigments of a similar type may be employed. Pigment in an amount up to 20 percent by weight of the rubber may be used, although percent is preferred.

The color of the eraser may also be varied by additions of other pigment material of suitable color. For example, it may be desirable to produce a blue-colored eraser, in which event any conventional blue pigment may be employed.

It is also necessary to employ certain additives such as antioxidants and curing agents. Such antioxidants and curing agents may be any of the substances known in the art, such as stearic acid, zinc oxide, 2-mercaptobenzothiazole, sulfur, etc. It is obvious that the optimum amount will vary with the type and amount of rubber used in perparing the eraser.

The following table sets forth several compositions which have formed satisfactory erasers. In each of these, the ingredients were intimately mixed and cured for 30 minutes at 307 F.

3. A noncrumbling eraser of a cured natural rubber composition consisting essentially of about 100 parts by weight of natural smoked rubber, to 80 parts by weight of polyisobutylene having a molecular weight not greater than 40,000, from 60 to 120 parts by weight of a mineral abrasive material possessing a hardness of from 7 to 9 on Mohs scale of hardness, and from 80 to 120 parts by weight of an inert filler material.

4. The eraser according to claim 3 wherein the mineral abrasive material is 100 to 400-grit size.

5. The eraser according to claim 3 wherein the mineral abrasive material is a ISO-grit size.

6. A noncrumbling eraser of a cured natural rubber composition consisting essentially of about 100 parts by weight of natural smoked rubber, from 30 to 50 parts by weight of polyisobutylene having a molecular weight not greater than 40,000, from 60 to 120 parts by weight of mineral abrasive material possessing a hardness of Table Parts by Weight Ingredients A B O D E F G H Smoked sheet natural rubber 100. 0 100.0 100.0 100. 0 100.0 100.0 100. 0 100.0 Vtstanex LM-S 40. 0 40. 0 40. 0 40. ll 40.0 40. 0 80.0 40.0 Silicon carbide (grit 150)- 0 60.0 40. 0 60. 0 80.0 120. 0 120.0 40.0 Silica flour 120. 0 0 80. 0 120. 0 120.0 80.0 80.0 80.0 'll-Pure R-110 n... 10. 0 10. 0 10. 0 10.0 10.0 10. 0 10.0 10.0 Phenyl beta naphth 1. 0 1. 0 1. 0 1.0 1.0 1. 0 1. 0 1.0 Stearic acid 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 1.5 1.5 1 Zinc oxide 4. 0 4. 0 4. 0 4. 0 4. 0 4.0 4. 0 4. 0 Captax 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 1. 5 Sulfur 3. 0 3. 0 3. 0 3. 0 3. 0 3.0 3. 0 3.0

1 Polylsobutylene having molecular weight of about 15,000. 1 Rutlle titanium dioxide. 3 Z-mercaptobenzothlazole.

The above examples illustrate a number of compositions applicable to the present eraser but should in no way confine the present invention to the exact composition set forth.

This application is a continuation-in-part of prior application Serial No. 356,298, filed May 20, 1953, now abandoned.

What is claimed is:

1. A noncrumbling eraser of a cured natural rubber composition consisting essentially of about 100 parts by weight of natural rubber, from 30 to 80 parts by weight of polyisobutylene having a molecular weight not greater than 40,000, and from 60 to 240 parts by weight of a mineral abrasive material possessing a hardness of from 7 to 9 on Mohs scale of hardness.

2. The eraser according to claim 1 wherein the cured natural rubber composition includes an inert filler material with the total amount of the mineral abrasive material plus the inert filler material being from 60 to 240 parts by weight.

from 7 to 9 on Mohs scale of hardness and having a grit size of from to 400, and from 80 to parts by weight of an inert filler material having an average particle size of less than 325 mesh.

7. The eraser according to claim 6 wherein the mineral abrasive material is silicon carbide and the inert filler material is silica flour.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A NONCRUMBLING ERASER OF A CURED NATURAL RUBBER COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 100 PARTS BY WEIGHT OF NATURAL RUBBER, FROM 30 TO 80 PARTS BY WEIGHT PF POLYISOBYTYLENE HAVING A MOLECULAR WEIGHT NOT GREATER THAN 40,000, AND FROM 60 TO 240 PARTS BY WEIGHT OF A MINERAL ABRASIVE MATERIAL POSSESSING A HARDNESS OF FROM 7 TO 9 ON MOHS'' SCALE OF HARDNESS. 